一个关于自定义标签的很诡异的问题

cwx_xp 2016-03-09 04:45:45
最近在做一个项目，项目中做了一个自定义标签，具体功能是根据用户ID查询用户所拥有的角色


public static String roleNames(Integer userid) {

        StringBuilder s = new StringBuilder();

        List<ReUserRole> reUserRoles =  getReUserRoleService().findByUserId(userid);//下面错误提示的Function.java:42

        for (ReUserRole reUserRole: reUserRoles) {

            Role role = getRoleService().findById(reUserRole.getRoleid());

            if (role == null) {

                continue;

            }

            s.append(role.getName());

            s.append("/");

        }

        if (s.length() > 0) {

            s.deleteCharAt(s.length() - 1);

        }

        return s.toString();

    }


后来平时调试时，发现一个很奇怪的问题：
每次我重启服务器之后，去访问用到这个标签的页面，有一定几率会报错（大概重启四五次会发生一次），错误信息如下：


HTTP Status 500 - An exception occurred processing JSP page /WEB-INF/view/user.jsp at line 246



type Exception report



message An exception occurred processing JSP page /WEB-INF/view/user.jsp at line 246



description The server encountered an internal error that prevented it from fulfilling this request.



exception



org.apache.jasper.JasperException: An exception occurred processing JSP page /WEB-INF/view/user.jsp at line 246



243:                     <td>${user.username}</td>

244:                     <td>${user.name}</td>

245:                     <td>${fn:organizationName(user.orgid)}</td>

246:                     <td>${fn:roleNames(user.id)}</td>

247:                     <td>

248:                         <shiro:hasPermission name="user:update">

249:                             <button class="btn btn-info btn-sm" data-toggle="modal" data-target="#updatePage"





Stacktrace:

	org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)

	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)

	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)

	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)

	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)

	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)

	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1244)

	org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)

	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)

	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)

	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)

	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)

	javax.servlet.http.HttpServlet.service(HttpServlet.java:621)

	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)

	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

	com.alibaba.druid.support.http.WebStatFilter.doFilter(WebStatFilter.java:123)

	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121)

	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

	org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61)

	org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)

	org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)

	org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)

	org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)

	org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449)

	org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365)

	org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)

	org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)

	org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:383)

	org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362)

	org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)

	org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)

	org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)

	org.jasig.cas.client.session.SingleSignOutFilter.doFilter(SingleSignOutFilter.java:100)



root cause



javax.el.ELException: Problems calling function 'fn:roleNames'

	org.apache.el.parser.AstFunction.getValue(AstFunction.java:124)

	org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:185)

	org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:1026)

	org.apache.jsp.WEB_002dINF.view.user_jsp._jspx_meth_c_005fforEach_005f3(user_jsp.java:969)

	org.apache.jsp.WEB_002dINF.view.user_jsp._jspService(user_jsp.java:210)

	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)

	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)

	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)

	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)

	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)

	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)

	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1244)

	org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)

	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)

	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)

	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)

	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)

	javax.servlet.http.HttpServlet.service(HttpServlet.java:621)

	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)

	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

	com.alibaba.druid.support.http.WebStatFilter.doFilter(WebStatFilter.java:123)

	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121)

	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

	org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61)

	org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)

	org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)

	org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)

	org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)

	org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449)

	org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365)

	org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)

	org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)

	org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:383)

	org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362)

	org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)

	org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)

	org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)

	org.jasig.cas.client.session.SingleSignOutFilter.doFilter(SingleSignOutFilter.java:100)
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接上面的错误信息 

root cause

java.lang.NullPointerException
	com.vastio.taglib.Functions.roleNames(Functions.java:42)
	sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	java.lang.reflect.Method.invoke(Method.java:597)
	org.apache.el.parser.AstFunction.getValue(AstFunction.java:112)
	org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:185)
	org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:1026)
	org.apache.jsp.WEB_002dINF.view.user_jsp._jspx_meth_c_005fforEach_005f3(user_jsp.java:969)
	org.apache.jsp.WEB_002dINF.view.user_jsp._jspService(user_jsp.java:210)
	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)
	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1244)
	org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
	com.alibaba.druid.support.http.WebStatFilter.doFilter(WebStatFilter.java:123)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61)
	org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
	org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
	org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
	org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
	org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449)
	org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365)
	org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)
	org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)
	org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:383)
	org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362)
	org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
	org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
	org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)
	org.jasig.cas.client.session.SingleSignOutFilter.doFilter(SingleSignOutFilter.java:100)

note The full stack trace of the root cause is available in the Apache Tomcat/7.0.42 logs.
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